In the episode where Joey is Al Pacino's butt double, there's a ceiling light hanging over the coffee table in the girls' apartment when they're making fun of Joey. But at the end of the episode, when he's explaining why they fired him, the light is gone.
Umm...the light just isn't in the shot. Think about it logically...why would the people set up the set take a ceiling light out or put one in? it's a permanent fixture on the set. It didn't move.